This invention relates generally to battery chargers and more particularly to battery chargers with protection circuitry.
The battery packs for portable power tools, outdoor tools and certain kitchen and domestic appliances may include rechargeable batteries, such as lithium, nickel cadmium, nickel metal hydride and lead-acid batteries, so that they can be recharged rather than be replaced. Thereby a substantial cost saving is achieved.
It is preferable to provide a charger that recognizes when a battery pack has been connected in order to begin charging.
In accordance with the present invention, an improved battery pack charger is employed. The charger includes a controller having an input and an output, a first terminal for connecting a battery pack to the controller, a connecting line disposed between the first terminal and the input of the controller, a current source connected to the controller for providing power to the battery pack, the current source providing the power to the battery pack via the connecting line, wherein the controller sends a pulse signal into the connecting line via the output, whereby the controller determines whether the battery pack is connected to the charger by the presence of the pulse signal in the input of the controller.
Additional features and benefits of the present invention are described, and will be apparent from, the accompanying drawings and the detailed description below.
The accompanying drawings illustrate preferred embodiments of the invention according to the practical application of the principles thereof, and in which:
The invention is now described with reference to the accompanying figures, wherein like numerals designate like parts.
Referring to FIGS. 1-2, a battery pack 10 is connected to a charger 20. Battery pack 10 may comprise a plurality of battery cells 11 connected in series and/or parallel, which dictate the voltage and storage capacity for battery pack 10. Battery pack 10 may include three battery contacts: first battery contact 12, second battery contact 13, and third battery contact 14. Battery contact 12 is the B+ (positive) terminal for battery pack 10. Battery contact 14 is the B- or negative/common terminal. Battery contact 13 is the S or sensing terminal. Battery contacts 12 and 14 receive the charging current sent from the charger 20 (preferably from current source 22, as discussed below) for charging the battery pack 10.
As shown in FIG. 1, the battery cells 11 are connected between the battery contacts 12 and 14. In addition, preferably connected between battery contacts 13 and 14 is a temperature sensing device 15, such as a negative temperature co-efficient (NTC) resistor, or thermistor, RT. The temperature sensing device is preferably in closer proximity to the cells 11 for monitoring of the battery temperature. Persons skilled in the art will recognize that other components, such as capacitors, etc., or circuits can be used to provide a signal representative of the battery temperature.
The charger 20 preferably comprises a controller 21, which in turn includes positive terminal (B+) 17 and negative (B-) terminal 18, which are coupled to battery pack 10 via battery contacts 12 and 14, respectively. The positive terminal may also act as an input, preferably an analog/digital input A/D, in order for the controller 21 to detect the battery pack voltage. In addition, the controller 21 may include another input TC, preferably an analog/digital input, which is coupled to the temperature sensing device 15 via the third battery contact 13 (S). This allows the controller 21 to monitor the battery temperature.
Controller 21 may include a microprocessor 23 for controlling the charging and monitoring operations. Controller 21 may control a charging power source for providing power to the battery pack 10, such as current source 22 that provides current to battery pack 10. This current may be a fast charging current and/or an equalization current. Current source 22 may be integrated within controller 21.
Controller 21 may have a memory 25 for storing data. Memory 25 may be integrated within controller 21 and/or microprocessor 23.
Controller 21 preferably has a pulse output PO, which sends a pulse signal into the same line that sends power to the battery pack 10. The pulse signal may have an amplitude of 5 volts. Preferably the pulse signal generated by the controller 21 goes through a diode D23 and/or a resistor R54.
With such arrangement, controller 21 can determine whether a battery pack 10 has been connected to the charger 20. FIG. 2 is a flowchart illustrating the process for determining whether a battery pack 10 has been connected to the charger 20.
First, the current source 22 must be off (ST1). The controller 21 then sends a pulse signal via pulse output PO (ST2).
The controller 21 then checks whether the input A/D has received a pulse (ST3). If a pulse was received, a battery pack 10 is not connected to the charger 20.
On the other hand, if a pulse was not received, the controller 21 would interpret this to mean that a battery pack 10 is connected to the charger 20. Persons skilled in the art will recognize that the voltage at input A/D will be substantially constant since resistor R54 and diode D23 will not allow a significant current to generate an AC signal across the battery. Since the pulse was not received, controller 21 would then start charging battery pack 10 by turning on current source 22 (ST4).
Controller 21 then senses the battery voltage V0 via input A/D (ST5). Controller 21 compares battery voltage V0 to a certain threshold X (ST6). If battery voltage V0 is below threshold X, charging continues and controller 21 continues to sense and compare the battery voltage V0.
If battery voltage V0 exceeds (or is equal to) threshold X, controller 21 then assumes that the battery pack 10 has been removed from charger 20 and stops charging by turning the current source off. Persons skilled in the art will recognize that it is preferable to provide a relatively high threshold so as to not prematurely terminate charging, resulting in an undercharged battery pack. Accordingly, it is preferable to provide a threshold of at least 30 volts.
FIG. 3 is an exemplary schematic diagram of the charger of FIG. 1. Preferably, the values of the different components of are as follows:
Persons skilled in the art will recognize that the pulse output PO and input are pins 15 and 7 of IC2, respectively. Persons skilled in the art will also recognize that diode D23 and resistor R54 are the same components in FIGS. 1 and 3.
Persons skilled in the art should recognize that the charger shown in FIG. 3 is connectable to a vehicle battery, rather than to an AC source. Nevertheless, persons skilled in the art will know how to modify the power supply within the charger to accept power from an AC source.